This proposal seeks funding to (1) capitalize on an extraordinary opportunity to develop massive new data infrastructure for the study of long-term demographic and economic change in the U.S. and (2) use these new data to investigate the demographic transformation of the U.S. in the second half of the 19th century. The investigators will collaborate with Ancestry.com to expand and enhance the complete-count 1850, 1860, 1870, and 1880 Integrated Public Use Microdata Series (IPUMS) census databases currently under construction at the Minnesota Population Center (MPC). The project will add 50 census fields not included in the initial data collection effort, such as occupation, wealth, school attendance, literacy, sickness, and disability. Individuals will be linked across the population, mortality, and slave census schedules and across the three intercensal intervals. These improvements will be added to IPUMS and freely disseminated for research and educational purposes. These data offer the earliest information available on key social and economic characteristics, and they will provide invaluable insight into processes of long-run demographic and economic change. The data will make a permanent and substantial addition to the nation's statistical infrastructure and will have far-reaching implications for research across the social and behavioral sciences. Leveraging this new resource, the project will undertake a comprehensive analysis of demographic change in the U.S. in the Civil War Era. Close examination of critical inflection points of demographic history is essential for evaluating demographic theory. The Civil War and emancipation of the nation's 4.5 million slaves was the largest demographic, economic, and social shock in U.S. history. The substantive component of the project focuses on three crucial issues whose consequences still resonate in 21st century society: the demographic costs and consequences of the American Civil War; African American demographic responses to emancipation; and the onset of the U.S. marital fertility transition. The project will be executed by a team of highly-experienced researchers with exceptional proficiency in large- scale data creation, integration, linkage, and dissemination and demographic analysis. It will leverage cutting- edge technology to process a vast volume of data at reasonable cost. The project is a collaboration of the MPC with the world's largest producer of genealogical data, allowing cost-effective use of scarce resources to develop shared infrastructure for population and health research.